You might think a stomach that lights up would be a liability when you're trying to avoid getting eaten — but the glowing bellies of tiny sharks are helpful in camouflaging them from predators lurking below, researchers say.

The smalleye pygmy shark (Squaliolus aliae), which lives in coastal waters of the southeastern Indian and west Pacific Oceans, only reaches up to 8.6 inches (22 centimeters) long. When silhouetted against weak light from above, these diminutive fish might appear to be easy prey. Hence the tiny light emitters that cover the undersides of these fish.

Velvet belly lantern sharks have glowing skin as well, using it for both camouflage and communication. The researchers find the pygmy sharks probably share an ancestor with the lantern sharks, since they regulate their glows in similar ways hormonally.

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The way that the pygmy sharks control their light systems also resembles the way shallow-water sharks control their skin color. This may show that the pygmy shark is "the missing link in the evolution of luminescence in sharks," shark researcher Julien Claes at the Catholic University of Louvain in Belgium told io9. The idea is that after shallow-water sharks evolved control over their skin pigment, pygmy sharks evolved control over glowing skin. Lantern sharks then developed even greater command.